Dehydrogenation catalyst



Patented Oct. 15, 1940 Herbert P. A. Groil,

Hamburg-Wellingsbuttel,

Germany, and James Burgln, Oakland, Oaiif., assignors to ShellDevelopment Company, San Francisco, Calif., a corporation of Delaware NoDrawing. Original application April 26, 1935, Serial No. 18,386. Dividedand this application July 4, 1939, Serial No. 282,812 1 8 Claims.

This invention relates to a novel process and catalyst for efiectingtheconversion of saturated hydrocarbons to olefinic compounds possessingthe same number of carbon atoms to the molecule. 5 More particularly,the invention relates to a catalytic dehydrogenation process whichcomprises contacting a paraflin hydrocarbon containing at least twocarbon atoms with a novel aluminum oxide-chromium oxide catalyst at anelevated temperature whereby said paraflin is dehydrogenated to thecorresponding valuable olefine.

It is an object of our invention to provide a practical and economicalmethod for the technical scale conversion of the saturated aliphatichydrocarbons, such as those contained in or derived from petroleumandpetroleum products, to the industrially valuable olefines.

The olefines of the aliphatic series are valuable raw materials for manypurposes. They are readily convertible into many products havingeconomic importance such as dichlorides, chlorhydrins, alcohols,glycols, ethers, esters, olefine oxides, etc. In addition, the olefinesand olefine polymers are useful as fuel and as components 25 impartinganti-knock qualities to fuel mixtures. Processes for effecting thedehydrogenation of hydrocarbons have been described in the literature.However, due to the difliculties of execution and the low yields ofunsaturated hydrocarbons commercial application.

It is known that at the highertemperatures, in the absence of catalyticmaterial, the paraflins pyrolyze and that olefines are formed therefrom.The mechanism of the pyrolysis involves, in addition to dehydrogenation,which occurs to a very limited extent, the disruption of the carbonchain resulting in the formation of saturated hydrocarbons and olefinespossessing fewer carbon atoms than the treated parafiin and in addition,under the high temperatures necessitated, considerable losses areoccasioned by carbon formation and polymerization.

invention is to effect substantial dehydrogenation while substantiallyavoiding losses due 7 to cracking.

Dehydrogenation can be effected, in the absence obtained, these-knownprocesses have not merited Accordingly, an'object of our active andtheir emcient use requires high space velocities and the use ofrelatively low temperatures if disruption of the hydrocarbon molecule isto be avoided. For example, nickel is a ver active dehydrogenationcatalyst yet it is unsuit-' able since its eiiicient use' requiresprohibitive space velocities and temperatures. so low that equilibriumconditions are reached when only a small amount of. the paraflin hasbeen dehydrogenated. Less active catalysts have been suggested butmarked disadvantages are also inherent in their use. The dehydrogenationcan be effected in the presence of alumina; however,

This catalyst is intermediate as propane, if substantial cracking is tobe avoided prohibitively high space velocities are necessitated and, asa consequence, the conversion is too low to be practical. For example,at high space velocities and a temperature of 400 C. the maximumconversion of propane to propylene is only about 4%. None of theproposed catalysts are suitable for the emcient and economicaltechnicalscale conversion of paraffin hydrocarbons v in general to thecorresponding olefines at practical space velocities and at temperaturesat-which the optimum conversions are attained. As a consequence; none ofthe processes hitherto proposed have merited technical application.-

Now we have found a novel catalyst for use in dehydrogenation reactions.Our. catalyst is a compound catalyst comprising aluminum and chromiumoxides with the former in substantial gravimetric excess of the latter.The catalyst functions as a true compound catalyst; it possesses theadvantageous features of both alumina and chromium oxide, while devoidof the properties which render the use of either of these oxides aloneundesirable. Its use provides a practical and economical process for theconversionv of paraiilns to olefines in hitherto unattainable yields. Wemay employ high space velocities and maintain a high production ofolefines per time unit while employing temperatures at which optimumpractical conversions are attained. Our

catalyst can be economically prepared from readily obtainable andinexpensive materials; it possesses suflicient stability and resistanceto poisoning withinthe desired temperature range and, in addition, whenits catalytic activity is impaired, it may be substantially restored toits initial activity readily and inexpensively. Our catalyst may beadvantageously employed under conditions of temperature and spacevelocity at which .by impregnating alumina, preferably in the porousstate, in any suitable solid form as powder, granules, pellets, etc.,with a chromic acid solution of suitable concentration depending uponthe desired chromic oxide content of the catalyst.

- Preferably the alumina is heated to about 300 C.

under a reduced pressure, then allowed to cool toabout room temperatureand the aqueous CIO: solution added while'the solid material is stillunder a reduced pressure. If desired, impregnation of the Ahoy-may beefiected by contacting it with the aqueous CrOa solution and alternatelyboiling and cooling. Prior to its use in the execution of the invention,the dried im-' pregnated material is'packed in .the required amount inthe reaction tube and heated to reaction temperature while the paramnhydrocarbon is passed through it at a suitable velocity. The hydrocarbonacts as a reducing gas when a sufficiently high temperature has beenreached and the CrOs is reduced to CrzOa.

Other suitable modes of preparing the catalyst will be apparent to thoseskilled in the art to which the invention appertains. Conditions ofpreparation should be such that the catalytic material is obtained in avery porous form, since physical structure may play a large part in itsefiectiveness. Our catalyst may or may not be used in the presence of asuitable substance capable of acting as a promoter.

We prefer to consider the catalyst with respect to its chromium oxidecontent expressed in per cent by weight of the catalyst mass. We mayadvantageously employ catalysts containing from about 6% to about 40% ofC1'203; but, in general the process is executed with catalystscontaining from about 15% to about 25% of CrzOa.

The AlzOa-Cl'sOa catalysts retain their activity over relatively longperiods of use. Loss of activity with use under normal conditions isusually due to decrease of surface and/or porosity caused by carbonand/or tar deposition which occurs to a small extent during thedehydrogenation. The initial activity of the fouled catalyst may bereadily and substantially restored by the simple andeconomical'procedure of passing air or another suitableoxygen-containing gas through the heated material for a sumcient time toefiect removal of the contaminating material by oxidation. The fouledcatalyst is preferably maintained at a temperature of from about 400 C.to about 700 C., in the dehydrogenating tube or another container, andair passed over it at an hourly space velocity of from about 600 to 900until the desired degree of activity has been restored. At a temperatureof about 500 C., virtually complete reactification usually requiresabout one hour.

The AhOa-Cl'sOz catalysts are preferably employed at temperatures offrom about 500 C. to about 700 C., although higher and lowertemperatures may, in some cases, be used. At lower temperatures, thecatalysts are less active and such long contact periods are required, ifa substantial conversion is desired, that cracking may occur to anundesirable extent. At temperatures substantially above 700 C.,impractical space velocities are essential if cracking is to besubstantially avoided. As a result, the

conversions .are too low due to the fact that equilibrium is notattained. Although, the catalyst may possess its optimum activity at thehigher temperatures, the rate of loss of activity is also greater,making the process generally more economically executed in the lowertemperature range at contact times favoring equilibrium'conditions andthe attendant high conversions.

The catalyst usually in granular form, is employed in manners customaryin dehydrogenation processes of this type. A quantity of said catalystmay be maintained in a suitable catalyst chamber at the desiredtemperature through which the treated material, preferably in the vaporphase, may be passed at the desired space velocity and under the desiredpressure. The

term space velocity as used herein may be defined as the unit volume ofgaseous material to be treated, measured at about 0 C. and atmosphericpressure, contacted with a unit volume of catalyst per hour. In theexecution of our invention, the space velocity employed when optimumconversions are desired is dependent upon the particular hydrocarbon ormixture of the hydrocarbon treated, upon the chromium oxide content ofthe catalyst and upon the temperature of execution.

Under optimum conditions of temperature and catalyst composition, a highconversion of propane to propylene is attained at space velocities offrom about 1200 to about 1500, while with the butanes a desired spacevelocity is from about'600 to about 840 and ethyl benzene isadvantageously treated at a space velocity of about 450.

With each particular hydrocarbon or hydrocarbon-containing mixturetreated, the temperature of execution and the chromium oxide content ofthe catalyst can be so regulated that we may employ a practical spacevelocity and obtain a practical conversion at a rate that is notdetrimental to the activity of the catalyst. When operating in thedesired temperature range, usually from 500 C. to 700 C., to obtain theoptimum conversion per passage of the gaseous material in contact withthe catalyst, the space velocity most advantageously employed isdependent upon the chromium oxide content of the catalyst. For example,the optimum space velocity increases as the chromium oxide content ofthe catalyst increases. When the catalyst contains less than about 6.0%of chromium oxide, such low space velocities are usually necessary thatthe conversion proceeds at an impractical rate and with excessive lossesdue to cracking. Catalysts containing more than about 40% chromium oxideusually require such high space velocities that their use is impracticalboth as regards the low conversions attained and the relativelyshorterlife of the catalyst.

The dependence of space velocity upon the chromium oxide content of thecatalyst to obtain optimum conversions per single pass may beillustrated with reference to results obtained in effecting theconversion of normal butane to butylenes. Comparative results wereobtained by passing previously dried gaseous n-butane through 35 cc. ofcatalyst contained in a l.l 33 cm. silica tube heated to 550 C. When thecatalyst contained about 6.0% chromium oxide, an optimum conversion of30% was obtained at a gas velocity of 110 cc./min. or a space velocityof 188.4. The same amount of catalyst containing about 40% chromiumoxide requireda gas velocity of about 500 cc./min. or a space velocityof about 858 to obtain a conversion of about 25%. In general, withhydrocarbons containing more than three carbon atoms, it appearsundesirable to employ space velocities much over 750 and, accordingly,we prefer to employ catalysts which render the use of such spacevelocities practical, that is, catalysts generally containing less than40% of chromium oxide.

A greater production of the corresponding olefine per time unit and perquantity 'of catalyst employed is attained when the higher spacevelocities are used; however, this advantage is offset by the lowerolefine content of the eiiiuent gas and by the relatively much shorterperiod of activityof the catalyst. The rate of loss of activity ofthecatalyst increases rapidly as the space velocity is increased. Lossof the activity of the catalyst in the absence of specific catalystpoisons is probably due to deposition of car bon on the surface thereofin accordance with the reaction CnI-I2n+2 nC+(n+l)I-Iz which reactionoccurs simultaneously with the dehydrogenation reaction but at a muchlower rate.

The velocity of this side reaction appears to be directly proportionalto the concentration of hydrocarbon in the reaction chamber and, ac-

cordingly, the rate of carbon deposition and the ratio of hydrogen toolefine is much greater at the higher space velocities and the rate ofac,- tivity loss of the catalyst is accelerated. Reactivation of thecatalyst as herein described comcatalyst consisting of aluminumoxide andchromium oxide is applicable with excellent results to the conversion ofsaturated hydrocarbons to unsaturated hydrocarbons. The same isparticularly applicable to the conversion of the paraflins to olefines.The parafins' containing a plurality of carbon atoms such as ethane,propane, the butanes, the pentanes, the 'hexanes, the heptanes and thelike may be treated by our method and converted in excellent yields tothe corresponding olefines. Such a straight or branch chain hydrocarbonmay be linked to a cyclic radical as of the aromatic, alicyclic seriesor the paraffin may comprise a saturated alicyclic structure. It is tobe understood that suitable substitution products of the above mentionedcompounds are also contemplated.

The saturated compounds may be treated sev erally or mixtures comprisingmore than one species of hydrocarbon may be treated. If desired,

mixtures of one or more species with a relatively inert'substance whichwill exist in the gaseous state under operating conditions are alsosuitable. For example, dehydrogenation may be effected the presence ofstable olefines, stable hydrocarbons, nitrogen, etc. The use of such aninert diluent provides a suitable means of increasing the conversion ofthe hydrocarbon treated by deadvantage'is more than offset by theadvantages attendant on the heat conductivity of the hydrogen.

, Another advantageous manner of decreasing the partial pressure of thetreated hydrocarbon comprises adding a suitable hydrogen acceptor to 4the hydrocarbon to be dehydrogenated. The dehydrogenation may beeffected in the presence of an unsaturated. hydrocarbon whose paramnequivalent is less easily dehydrogenated than the compound treated. Forexample, sufiicient ethyl-.

ene may be mixed with a hydrocarbon higher than ethane so that thehydrogen liberated from the treated hydrocarbon hydrogenates theethylene to ethane. The hydrogen acceptor is chosen .with respect to thehydrogen donator and employed under such conditions that the former ismore readily hydrogenated than the dehydrogenation product of the latterwhile the hydrogenation product is less readily dehydrogenated than thehydrogen donator.

Another suitable means of decreasing the partial pressure of the treatedhydrocarbon comprises effecting the dehydrogenation under a sub-'atmospheric pressure.

The process may be applied to substantially pure hydrocarbons ormixtures thereof or to their mixtures such as occur in petroleum,natural gas, etc. Suitable hydrocarbon mixtures may be obtained by thedestructive distillation or'hydrogenation of coal, peat, pitches, tars,etc., as well as by the pyrogenesis of petroleum, petroleum products,shale oils, etc., as well as from the extraction, distillation,transformation and the like products of the same. Highly saturatedhydrocarbon motor fuels such as gasoline containing but small amounts ofoleflnes, can be improved in accordance with our process by passing thesame over the catalytic material under the conditions herein specified;In this manner, the amounts of unsaturates in the fuel can be increasedand its anti-knock qualities enhanced.

Technical paraflin-olefine-containing mixtures such as thepropane-propylene cut, the butane butylene cut, the pentane-amylenecut,etc., may be treated by ourmethod and the ratioof olefine to paraffinincreased, or such a cut or the original mixture may be treated by anysuitable means such as fractionation, condensation, absorption,extraction and the olefines removed therefrom prior to treatment by ourmethod.

While our invention has been described with particular reference to itsuse as a means of dehydrogenating saturated hydrocarbons to thecorresponding oleflnic compounds, it is to be understood that the sameis also applicable with excellent results to the dehydrogenation ofunsaturated hydrocarbons to still more unsaturated compounds. Forexample, by our method, cyclohexene and cyclo-hexadiene may bedehydrogenated to benzene, tetrahydronaphthalene to naphthalene, etc.

The following examples are introduced for the purpose of illustratingmodes of executing our invention and the results thereby attained, butthe invention is not to be considered as limited to the specificmaterials or conditions specified therein.

Example I An aluminum oxide-chromium oxide catalyst was prepared byimpregnating granules of porous calcined alumina with chromic acid.About 35 cc. of this catalytic material was packed in a quartz reactiontube having an inside diameter of 10.4 mm. and heated over a length ofabout cms. The tube was heated to about 575 C. while propane was passedthrough it to reduce the CIO: to CrzOa. The resulting catalyst masscontained about 20.0% of CrzOa.

The catalyst mass was maintained at a temperature from about 575 C. toabout 585 C. while propane was passed through it at a space velocity offrom 1200 to 1500 for a period of two hours. The average conversion ofpropane to propylene was about 30%. At the end of four hours the averageconversion was 26.3%.

After four hours of conversion, the catalyst was regenerated by passageof air over the catalyst mass at a space velocity of from about 600 to720 and a temperature of about 580 C. The catalyst was substantiallycompletely regenerated by treatment for about one hour. With theregenerated catalyst, an average conversion of about 25.1% was obtainedover a period of about four hours. 1

Example 1! Normal butane was passed over about 35 cc. of aluminumoxide-chromium oxide catalyst containing about 17% of chromium oxide inthe form of the chromium oxide CrzOa. The gaseous butane was passed atspace velocity of from about 600 to 720 (gas velocity about 330 to 440cc./min.) over the catalyst contained in a quartz tube having an insidediameter of 1.3 cm. and heated to a temperature of about 540 C. toabout-5 0 C.

The results of this experiment are shown in the following table:

- Butane passed through tube=51.0 liters Average conversion tobutylene=31.0% Volume of butylenes produced=15.8 liters Butylenesproduced/gm. catalyst= .13 Butylene content of eflluent gas=23.3%

Composition ,of effluent gas-(By weight) Butane=60.0%

Butylenes=29.5%

Hydrogen=1.5%

Other saturated and unsaturated hydrocarbons=9.0%

The experiment was run in cycles of conversion and regeneration. Whenthe conversion of butane to butylene reached about 25%, the catalyst wasregenerated by passing air over it at a space velocity of from 600 to720 at a temperature of about 550 C. for about one hour. The catalystafter a great many regenerations only showed a slight decrease inactivity.

Straight pyrolysis of normal butane in the absence of a catalyst yieldsonly 5% of butylene;

the main reaction'comprislng splitting to form methane, propylene,ethane and ethylene.

Example III An aluminum oxide-chromium oxide catalyst was prepared byheating granules of A: at a temperature of about 300 C. for about onehour under a subatmospheric pressure. The A1203 was cooled and, whileit-was still under a reduced pressure, an aqueous solution of CrOa wasadded thereto. The dried catalyst was packed in a quartz tube and heatedto a temperature of about 550 C. while isobutane was passed through toconvert the CrOa to CraOs. tion was complete, the catalyst masscontained about 17% CIzOa.

The dehydrogenation was effected by passing isobutane, at a spacevelocity of about 756, over the Al2OaCr2O3 catalyst maintained at atemperature of about 550 C. Over a period of two hours, an averageconversion of about 34% isobutane to isobutylene was effected. After twohours of continuous operation the catalyst was regenerated with air atabout 550 C. for one hour. Approximately the same conversion wasattained with the regenerated catalyst.

Example IV Example V Ethyl benzene vapor was passed over an aluminumoxide-chromium oxide catalyst, containing from 17% to 20% chromiumoxide, heated to a temperature of about 630 C. The ethyl benzene vaporwas passed over the'catalys't at a space velocity of about 450. About 84gm. of ethyl benzene were passed through the reaction .tube and 74.6 gm.of liquid condensate were collected. Distillation of the condensedliquid showed'that a yield of about 25% styrene was obtained on onepassage of the ethyl benzene over the catalyst. The bottoms of thedistillation consisted of a gum-like resin which was probably a styrenepolymer or condensation product.

When the reduc-' Our invention may be executed in a batch, in-

munication with the storage vessel containing the material to be treatedand utilize one or more reaction units while one or more are out of use.When the catalyst loses its activity to the extent that the conversionper pass is no longer practical, the material to be treated is divertedto the reactors not previously used or to those containing activatedmaterial. While. conversion is efiected in one or more dehydrogenatingunits, the used catalytic material in others may be .regenerated withair. The exit gases can be conveniently used inthe production ofalcohols by having the dehydrogenating units in communication with anabsorption unit wherein the olefines present are absorbed in asolutionof a strong mineral oxy-acid such as sulfuric and the like.Gases thus partially or substantially denuded of olefines can then 'berecirculated through the conversion units. Alternatively the exit gasesmay be substantially freed of hydrogen by bringing them into contactwith a suitable hydrogen-binding material such as an easily reduciblemetal oxide as CuO, etc., and the treated gas recirculated untilsubstantially complete conand the appended claims are intended toexelude those reactions in which oxygen or its version to unsaturateshas been effected. If desired a suitable hydrogen-binding agent capableof reacting with hydrogen under dehydrogenating conditions maybepresent. It is seen that ourprocess also provides a novel process forthe production of hydrogen which gas is useful for a wide variety ofpurposes.

While we have described our novel catalystwith particular reference toits use as an agent for accelerating the dehydrogenation oforganicequivalent combines with a hydrogen-containing compound to form acompound containing less hydrogen. Such reactions are entirely differentfrom the type of reaction'which occurs in accordance with our invention,whereby hydrogen atoms are split from hydrogen-containing compoundsresulting in the production of an unsaturated compound and molecularhydrogen.

This application is a ing application, Serial No. 18,386, filed April26,

Our catalyst may. be-

division of our copend-- 1935, which matured into United States PatentNo. 2,184,234 on December 19, 1939. v 7

While we have described our invention in a detailed manner and providedspecific examples illustrating suitable modes of executing the same,

it is to be understoodthat modifications may be.

made and that no limitations other than those imposed by the scope ofthe appended claims are intended.

We claim as our invention:

1. As a. dehydrogenation catalyst: an intimate mixture of aluminum oxideand chromium oxide comprising calcined alumina and chromium oxideincorporated in the surface of said alumina and present in the amount offrom 15% to 25% of the catalyst mass. v

2. As a dehydrogenation catalyst, an intimate mixture of aluminum oxideand chromium oxide I comprising calcined granular alumina and depositedchromium oxide adherent to each granule, the catalyst mass containingfrom about 6% to 40% chromium oxide.

3. As a dehydrogenation catalyst: a mixture of the oxides of aluminumand chromium comprising alumina and chromium oxide incorporated in thesurface of said alumina and present in the amount of from 6% to about40% of the catalyst mass.

4. As a dehydrogenation catalyst: a.v mixture essentially consisting ofthe oxides of aluminum and chromium and containing from 15% to 25%chromium oxide calculated as CrzOz.

5. As a catalyst: a mixture essentially consisting of the oxides ofaluminum and chromium and comprising an aluminum oxide impregnated withfrom about6% to about 40%, of the catav lyst mass, of a chromium oxide.

6. As a catalyst: a mixture essentially consisting of the oxides ofaluminum and chromium and containing from, 6% to 40%'by weight ofchromium oxide.

'7. A compound catalyst essentially consisting of oxides of aluminum andchromium, in which combination each oxide is present in a substantialamount with the aluminum oxide predominating over the chromium oxide byat least the ratio of 1.5 to 1 by weight.

8. A dehydrogenation catalyst which ,essen- 'tially consists of aluminumoxide and an oxide.

of chromium, and was formed by the addition of chromium trioxide tothealuminum oxide."

, HERBERT P. A. GROLL.

JAMES BURGIN.

